This invention relates to a method for growing a silicon thin film on a semiconductor single crystal substrate.
As the method for growing a silicon thin film on a semiconductor single crystal substrate, there has been used a method in which with a silicon raw material gas supplied, a silicon thin film is grown on a semiconductor single crystal substrate by a vapor phase growth process.
FIG. 1 shows an example of the apparatus for fabricating silicon thin films. For forming a silicon thin film with this apparatus, a semiconductor single crystal substrate 1 such as a silicon semiconductor single crystal substrate is placed in a process vessel (reaction vessel) 10 made of quartz glass or the like, and infrared light is irradiated to the semiconductor single crystal substrate 1 by energizing an infrared lamp 11 provided outside the process vessel 10, so that the temperature of the semiconductor single crystal substrate 1 is increased to a desired temperature, for example, 950.degree. C. or 1000.degree. C. Then, a silicon raw material gas 3 given by a dilution gas such as hydrogen gas diluted with trichlorosilane (SiHCl.sub.3) or the like is introduced through a gas inlet 12, by which a silicon thin film such as a silicon single crystal thin film or the like is grown on a surface of the semiconductor single crystal substrate 1 maintained at the high temperature. Also, for adjustment of the resistivity of the silicon thin film, diborane gas (B.sub.2 H.sub.6) or phosphine gas (PH.sub.3) or the like is introduced together. As the silicon material, dichlorosilane (SiH.sub.2 Cl.sub.2) or silicon tetrachloride (SiCl.sub.4) may be used, in some cases, instead of trichlorosilane (SiHCl.sub.3).
In addition, for prevention of silicon deposition on the wall of the process vessel 10 due to the reaction of the silicon material, the temperature of the wall of the process vessel 10 is controlled by absorbing heat from the process vessel 10 by making a flow of a coolant 4 such as low-temperature air or nitrogen gas. The temperature of the semiconductor single crystal substrate 1 is measured, for example, by a radiation thermometer 2 provided outside the process vessel 10.
It has conventionally been known that, in the method for growing a silicon thin film by supplying a silicon raw material gas formed by diluting hydrogen gas with trichlorosilane (SiHCl.sub.3) as described above, trichlorosilane (SiHCl.sub.3) decomposes into SiCl.sub.2 in vapor phase, which is an important reaction intermediate that accelerates the principal chemical reaction in the growth of the silicon thin film. Further, it has also been reported that silicon tetrachloride (SiCl.sub.4) is generated in association with this reaction (for example, J. Nishizawa and M. Saito, J. Crystal growth, Vol. 52, pp. 213-218, 1981).
Silicon tetrachloride (SiCl.sub.4), which, once formed, is relatively stabler to heat than trichlorosilane (SiHCl.sub.3), decreases in the rate of contribution to the formation of the silicon thin film, which has been a cause of reducing the supply efficiency of the silicon material. Also, silicon tetrachloride (SiCl.sub.4) yields large numbers of hydrogen chloride molecules each time one silicon atom from one molecule thereof is contributed to the growth of the silicon thin film, which has been a cause of undesirable results such as the formation of small voids at the surface of the silicon thin film.
Therefore, an object of the invention is to provide a method for fabricating a silicon thin film with a high supply efficiency of silicon material.